Sand muller

[Pete O]

I've been wanting to build a muller for a while, had a few bits put aside waiting for the right time. I had to cancel an outback trip due to COVID lockdown so made a start on the muller and I've been spending some time on it over the past week.

The base is a chunk of 12mm plate that came from a clearing sale. Should take a while to wear through that. A geared motor came from a friend who installs medical imaging equipment, think it was off the table lift for an MRI machine or similar. The motor is a flange mount so I bored a suitable hole in the plate to mount it
   
   

The output is 600RPM and I'm using a double-reduction belt drive to target about 50RPM in the muller. Cobbled together a countershaft assembly from some channel out of the scrap pile, a pair of flange-mount bearings and 1" shaft
   
   

This thing was on the motor that I used for my rotary phase converter, it seems to be cast steel and I've kept it aside for a muller wheel since building the RPC
   
This is the general arrangement idea with the wheel cut off that casting and the big pipe offcut that will be the body of the muller.
   
The central hub thingamajig that will have the wheel and scrapers suspended from it was fabricated using another bit of heavy-walled steel pipe that I grabbed from the scrappy for a crucible. It will form  an umbrella over it's own hub bearing, I plan to be able to break out my poured moulds straight into the muller so everything has to be protected from sand from above. this is the hub assembly having a keyway cut in the shaper.
   

I've seen a couple of builds on youtube with a trapdoor in the base for emptying the sand into a bucket; that seems like a better idea than having to tip this thing out considering it will weigh more than me by the time it's finished. I cut an opening in the base plate
   
then mounted the plate in the mill and beveled the opening
   
   

then set the same cutter up in horizontal mode on the frankenmill to bevel the sliding piece
   

The setup was nice and repeatable so I could test fit and sneak up on the finish width
   
   

then round the end and bevel the curve on the belt grinder to close the hole.
   
   

Will post more as I make more.

[Highpower]

(06-12-2021, 05:27 AM)Pete O Wrote:

I was looking at your counter-shaft assembly and was wondering why it had a shaft with a pointy end on it?  

Yet it was vaguely familiar and after looking at it for awhile all of a sudden it dawned on me. I have nearly the very same thing hanging on my shop wall right now!

It's my lawnmower blade balancer.  

[Pete O]

I had that piece of 1" round in my rack for ages- I vaguely recall putting a point on it but can't remember what for. Other than the main drum that I scrounged for the purpose ages ago, four belt pulleys and the four bearings, so far this whole thing has been designed and built around what scrap and offcuts I have on hand.

[Highpower]

"Nothing too strong ever broke." ~ Tom Lipton

I think that pretty much sums up everything you build Pete.

[Pete O]

Some more progress on the Mullmaster (a working title!).
Got the drivetrain completed, the spring-loaded tensioner on the second-stage belt is off a multi-ribbed belt drive from one of my cars; it'll be interesting to see how long the belt holds up being bent so far backwards but at least it gives it a good wrap around the 2" drive pulley.
   

Had a hunt around the scrap piles to see what I could come up with for legs- an old Range Rover drag link was long enough for one pair and a chunk of rebar for the other pair.
   

I had an offcut from the sheetmetal work on my daughter's pottery wheel that was sufficient for the paddles and the emptying chute, attached the pair of paddles to the hub with some scraps of gal angle (the mig really doesn't like that stuff), put a tub under the chute, wired a plug to the motor and gave it a test run.
Going to have to cut the outside paddle down a little both ways, it threatens to throw sand over the wall as well as leaving too narrow a windrow for the wheel. With the gate open, it empties itself pretty well.
   
   
   
The speed is less than it looks in the photo- shutter speed was slow due to low light. I'll try and remember to put my RPM gauge on it but it seems a pretty good speed.

Next job is to install the roller; going to be a bit problematic as I was planning on using a trailer hub and stub-axle but we are in lockdown again so I can't source anything other than what I have lying around.

[Pete O]

I got the wheel made and mounted yesterday evening- will post some pics when time permits- and encountered a bit of a setback. With the wheel installed, when the muller is loaded with sand the second stage belt drive slips and stalls the drive. Not entirely unforeseen, but a bit disappointing as I will have to swap the pulleys and belt for a chain drive on the second stage.

[Pete O]

I've managed a few more short sessions on the muller build since the last update. Firstly i converted the second stage of the drive to a chain and sprockets which solved the slipping belt problem; plenty of drive power now and no stalling of the mechanism. Rotation speed of the muller is 56 RPM.
   

The paddles have taken quite a bit of sorting out; my original outside paddle was way too flimsy (above quote notwithstanding) so I cobbled together a more sturdy arrangement with some 50x5mm flat bar welded onto a 20mm rod of forgotten origin. I initially attached it to the same radial member as the wheel is attached to and it all appeared to work well until I started to add some moisture to the dry sand that was being mixed...the paddle was too close to the wheel and it all just formed a bolus that went around and around without mixing. Tonight I made another mounting bracket for the outer paddle and finally it all works properly.
   

The steel pipe offcut that I used for the muller body turns out not to be quite round so the outer paddle doesn't seep the whole perimeter but I can live with that.

I did a trial run with a batch of sand and it seems that 3 buckets full is about the comfortable batch size. Did two batches in about 5 minutes each, mixed dry first and then slowly adding water to taste. Very happy with the result, a consistent blend through the batch. I can get two batches into this feed tub under the chute, this is a little under half my greensand supply.
   
   

Lots to do before I'll consider it finished but I'm now happy that 'eet weel mull'.